Many effective anthelminthics inhibit muscle contraction, either by directly interfering with processes at the neuromuscular junction or inhibiting energy metabolism. Since the mitochondrial metabolism of many parasitic helminths is predominantly anaerobic and differs substantially from that of the host, it is a potential site for chemotherapeutic attack. During the previous grant period, a number of important insights into the regulation of the enzymes involved in the mitochondrial metabolism of the parasitic nematode, Ascaris suum, have been described. The present study is designed to extend these studies and concentrate on differences that have been identified between host and parasite. Specifically, a novel component of the ascarid pyruvate dehydrogenase complex (PDC) will be further characterized and its role and that of E2 acetylation in the regulation of PDC activity by its associated kinase and phosphatase will be identified. In addition, the regulation of NADH-dependent 2-methyl branched-chain enoyl CoA reduction will be characterized using submitochondrial particles and purified ascarid enzymes, and the generation of a proton-gradient and ADP phosphorylation measured directly. Since Ca++ appears to play a unique role in the regulation of ascarid mitochondrial metabolism, Ca++ fluxes in isolated ascarid mitochondria will be measured and correlated with end-product formation and energy- generation. Preliminary experiments have suggested that mitochondrial volume is an important regulator of organic acid formation in these isolated mitochondria so that its role also will be described. These studies will permit the development of well characterized preparations of ascarid mitochondria, capable of volatile organic acid synthesis at physiological levels, and should provide a much clearer picture of energy-generation in these often studied, but still poorly understood organelles. Since these mitochondria are often used to screen compounds for potential anthelminthic activity, a clear understanding of their function is essential to intercept results meaningfully, especially since they differ so profoundly from the corresponding mammalian organelles.